Water and associated contaminants seep into the ground and travel through a subsurface region known as the vadose zone (a region of unsaturated soil). How the water and associated contaminants move in the vadose zone, to a large degree, determines how much contamination (such as gasoline additives, agricultural chemicals, or buried waste leakage) may end up in a water supply (such as an aquifier). Therefore, gaining an understanding of how the water and associated contaminants move in the vadose zone is valuable for appropriate waste containment. Information regarding the movement of water and associated contaminants in the vadose zone is generally acquired through the use of subsurface probes or similar testing devices. Several apparatus and methods have been used to facilitate such testing and information gathering. Some of these apparatus and methods involve obtaining samples of subsurface liquids, while others test soil moisture or other parameters.
In regard to sampling subsurface liquids, various methods and apparatus have been employed, including extraction of a soil core, introduction of vacuum-based or absorptive devices or materials, use of suction lysimeters, solution samplers, and other methods. Although there are several types of lysimeters, the term “lysimeter,” will be used in this document to refer to a suction lysimeter.
The suction lysimeter is a hydrological instrument used to sample liquids or to monitor soil or like substrates. The lysimeter accomplishes this function by application of vacuum or pressure gradient principles such that the liquid of interest is drawn toward the lysimeter permitting collection of a liquid sample. Although the lysimeter is primarily a sampling device, it may also be used to provide an indication of the water pressure (positive or negative). This is done by applying a vacuum, allowing the sampler to pressure equilibrate with the surrounding material being sampled, and recording this pressure.
Although prior lysimeters have been useful in gathering much information, such lysimeters have several shortcomings which have limited their usefulness. For example, prior lysimeters cannot be installed without prior excavation or drilling, and in contaminated areas such excavation or drilling is highly undesirable as it would tend to spread contamination. Additionally, such lysimeters have provided only small samples of subsurface liquids.
Another problem is that lysimeters are very fragile. They are made of ceramic, tin, copper, plastics, or similar such materials and cannot be installed directly through difficult materials such as hardened soils, concrete, steel, other metals, or waste products.
Monitoring and testing to determine the movement of subsurface water and associated contaminants is particularly valuable when dealing with waste disposal sites that contain radiological contaminants or other hazards. However, as described above, placing probes into the subsurface for data collection in such sites has not been feasible, because the placing of such probes would require drilling or coring which would bring contaminated “cuttings” to the surface and would create a pathway through which contaminated emissions may escape. As a result, test probes have typically been placed in areas around such waste sites. Unfortunately, such probe placement only provides information when the contaminants have already migrated outside of the waste disposal site area. Moreover, at the point when the contaminants have already migrated outside of the waste disposal site area, it is likely that a major contaminant plume already exists in the subsurface soil and aquifer making remediation and containment efforts much more difficult and costly.
In view of the foregoing, it would be highly desirable to provide methods and apparatus which facilitate subsurface testing and sampling in both contaminated and non-contaminated areas, while substantially avoiding these and other shortcomings of the prior devices.